This project will continue a long-term interdisciplinary project that studies the relationship between population, agricultural land use, and environment in the Great Plains of the U.S. Earlier phases of this project have led to the development of data bases and an interdisciplinary research team, and to the publication of important research findings. It has also revealed rich opportunities for continued research. Building on a large data base created in earlier phases of the project, the proposed research will develop a sample of land use and land cover (LULC) data across the region based on interpreted aerial photography and satellite imagery, for the time period from the 1930s through 2005. This deep time series of LULC data will enable us to develop specific hypotheses and to investigate the role of scale in each. The key thesis asserts that a substantial portion of the Great Plains region has never been converted from grassland to cropland. The LULC data will allow us to test whether the spatial location of agriculture has remained fixed, despite the tremendous adjustment of farm size in the region since the 1940s. The new data will also be used for other analyses, including land use change associated with irrigation, demographic change and the abundance and diversity of wildlife. The LULC data will also enhance a body of research that relates the history of family formation and population dynamics to variations in the scale of environmental impacts and change. The research will also build on a newly-created set of biogeochemical models for the entire region to produce region-wide and sub-regional long-term carbon and nitrogen budgets. The nutrient budget research will allow the investigators to study issues of scale in human-environment interactions by exploring the relative impact of changes in the environment that are driven by local population change (such as urbanization and suburbanization), as opposed to global changes that drive markets (for example those that spur the growth of livestock production or irrigated agriculture).